Tapeworm - To Treat or To Test?

Rachel Mallet, BVM&S MRCVS, is a qualified Veterinary Surgeon, who now works as a Professional Services Vet; providing technical support to vets, SQPs and horse owners in the UK. Rachel is passionate about animal health and about promoting best practice among animal health professionals and horse owners. Here, Rachel talks about the best-practice approach to addressing a parasite which all horse owners will be familiar with tapeworm.

For horse owners, the arrival of Spring is synonymous with tapeworm treatment. In general, horse owners in the UK have willingly adopted a strategic approach to worming based on faecal eggs counts (FEC). However, many are reluctant to adopt the same approach to tapeworms and continue to treat twice annually in spite of not having information about the infection status of their animal. On continuation, I provide some information about this common parasite, and best practice methods to address it.

The Equine Tapeworm

There are a number of species of tapeworm in the UK which are capable of infecting horses; however most of these are rare. The tapeworm species most commonly found in the horse is Anoplocephala perfoliata. It can reach up to 8cm in length and attaches itself to the intestinal lining at the ileocaecal junction which is where the small intestine meets the large intestine. It Is a perfect location for the tapeworm because the digestive juices found here are rich in the nutrients which it needs to thrive.

How Common is Tapeworm Infection?

It is impossible to be certain of infection rates due to the difficulty in detecting infection but studies suggest up to 69%1 of horses in the UK are infected at any given time.

A horse can become infected at any age; however tapeworm tends to have a bigger impact on very young and very old horses as their immune systems are not as robust.

Life Cycle

The tapeworm has an indirect life cycle which means that it requires more than one host to reach adulthood and reproduce.

The intermediate host for the most common equine tapeworm (A.perfoliata) is the forage mite (Oribatid mite). Forage mites are found on pasture and play a vital role in maintaining good quality grazing. The mites themselves pose no threat to your horse but the tapeworm cysts which they carry can.

Your horse can ingest forage mites when grazing at pasture or from conserved forage such as hay. If these forage mites are infected they can transmit the tapeworm cyst to your horse. The cyst is then ‘digested’ to free the infective tapeworm which attaches to the intestinal lining at the ileocaecal junction.

As the tapeworm grows it develops body segments, andonce it reaches sexual maturity these segments fill with eggs and are shed in the faeces. It takes 6-10 weeks after the horse ingests the cyst for the tapeworm to begin shedding eggs.

Clinical Signs of Tapeworm Infection

It benefits the tapeworm to cause as little damage to its host as possible, in order to ensure it maintains its source of nutrition. For many years it was believed that tapeworms cause no real problems in horses. However, more recent studies have shown that they can be linked to spasmodic colic, impaction at the ileocaecal junction, ileocaecal intussusception, intestinal ulcers and peritonitis.

Your horse may be infected with tapeworm and show no symptoms at all. In more severe infections they may have some of the following clinical signs:

Diarrhoea

Dull Coat

Poor Growth

Intermittent Colic Episodes

Poor performance

General Lethargy

Diagnostics

We know from the tapeworm life cycle that when the tapeworm sheds its eggs they are dispersed in a segment of its body called the proglottid. If the proglottid remains intact then no eggs will be found in the faeces in spite of the horse being infected. As a result tapeworm eggs are rarely detected in faecal egg counts (FEC) even if the horse is infected.

The best approach is to carry out a test called an ELISA antibody test. When a horse becomes infected with tapeworm it will produce antibodies to try and protect itself. The ELISA test is capable of detecting these antibodies. It could previously only be carried out on a blood sample but can now be carried out on saliva making it much more accessible and cost effective. The antibodies persist for months after an infection so a positive result tells us that the horse has been exposed to tapeworm recently. A positive result and a lack of recent tapeworm treatment allows us to assume that the horse is infected.

Ideally you should carry out an ELISA test before treating for tapeworm to help protect our wormers from resistance.

If you are unable to test you should carry out tapeworm treatment once in the Spring and once in the Autumn.

The two active ingredients which can treat tapeworm infection are Pyrantel Embonate (double dose) and Praziquantel. Table 1 details the activity of the anthelmintics which are available to treat tapeworm in horses.

Remember to give your horse the correct dose for its weight- you can use a weigh bridge or a weigh tape to determine the dose required. Repeatedly exposing parasites to the same class of anthelmintic is known to speed up the rate of resistance so try to rotate the class of active ingredient which you use. Remember to consider which parasites you are trying to target and select the most appropriate active ingredient based on that.

If you are uncertain please speak to your vet or SQP as they will be able to give you the best advice for your circumstances.

Table 1

Parasites Treated

Pyrantel

Praziquantel

Ivermectin / Praziquantel

Moxidectin / Praziquantel

*Pyrantel must be administered at a double dose to effectively treat tapeworms

Tapeworm

*

Small Strongyles

Encysted Small Redworm

Large Strongyles

Large Roundworms

Pinworms

Habronema muscae

Hair Worms (Trichostrongylus axei)

Bot Fly

Neck threadworms (Onchocerca spp)

Intestinal threadworms (S. westeri)

Lungworm

References

D.W.Jagger et el (1988). “Prevalence of Anoplocephala perfoliata in horses and ponies in Clwyd, Powys and adjacent English marches” Vet Record 123 562-3

Care should be taken to avoid the following practices because they increase the risk of development of resistance and could ultimately result in ineffective therapy:

Too frequent and repeated use of anthelmintics from the same class, over an extended period of time.

Under dosing; this may be due to underestimation of body weight or mis-administration of the product.

This information was provided by Bimeda- makers of Bimectin Equine1 and Embotape21Bimectin Equine (18.7mg/g Ivermectin) is a POM-VPS medicine.2Embotape (11.4g/syringe Pyrantel Embonate) is a POM-VPS medicine. For full product information including dose rates, see the SPC data sheet on the VMD website or the data sheet on the Bimeda Website Use Medicines Responsibly. Noah.co.uk